1. Field of the Invention
The present invention relates to a method for adjusting the temperature characteristic of a vibrating gyroscope, and more particularly, to a method for adjusting the temperature characteristic of a vibrating gyroscope used for preventing camera shake or used in a car navigation system and a pointing device.
2. Description of the Related Art
FIG. 8 is a perspective view of a vibrating gyroscope serving as a background of the present invention. A vibrating gyroscope 1 includes a vibration member 2. The vibration member 2 is formed by joining a first piezoelectric substrate 3 and a second piezoelectric substrate 4. The first piezoelectric substrate 3 and the second piezoelectric substrate 4 are polarized in opposite directions to each other in the thickness direction as shown by arrows in FIG. 8.
On the outside main surface of the first piezoelectric substrate 3, a divided electrode 5 is formed. The electrode 5 is divided into two sections in the width direction by a groove extending in the longitudinal direction of the first piezoelectric substrate 3. The electrode 5 is further divided into three sections in the longitudinal direction by two grooves extending in the width direction of the first piezoelectric substrate 3. In this way, the electrode 5 is divided into six sections. On the whole surface of the outside main surface of the second piezoelectric substrate 4, another electrode 6 is formed.
In this vibrating gyroscope 1, a driving signal is applied between two electrode sections 5a and 5b disposed at the center in the longitudinal direction of the electrode 5 and the electrode 6, which is disposed opposite the electrode 5. Since the first piezoelectric substrate 3 and the second piezoelectric substrate 4 are polarized in opposite directions to each other, the vibration member 2 has a bimorph structure. When a driving signal is applied, the vibration member 2 bends and vibrates in the direction perpendicular to the surfaces on which the electrodes 5 and 6 are formed, with two nodes disposed a short distance inside from both ends in the longitudinal direction serving as center points. Since the electrode sections 5a and 5b output the same signal during vibration, if a difference is measured between the signals output from these electrode sections 5a and 5b, the difference is zero because the two output signals are offset.
When the vibration member 2 is rotated about its axis, a Coriolis force is generated in the direction perpendicular to the direction in which the vibration member 2 bends and vibrates. Therefore, the direction in which the vibration member 2 bends and vibrates changes, and the output signals of the electrode sections 5a and 5b vary. In other words, when the signal output from an electrode section 5a increases in response to the Coriolis force, the signal output from the other electrode section 5b decreases in response to the Coriolis force. Therefore, only the signal corresponding to the Coriolis force can be obtained from the difference of the output signals of these electrode sections 5a and 5b. In this way, by measuring a difference between the output signals of the electrode sections 5a and 5b, a rotation angular velocity which the vibrating gyroscope has is detected.
Such a vibrating gyroscope has, however, a temperature characteristic for each output as shown in FIG. 9. In other words, a drift voltage output from the vibrating gyroscope increases and decreases according to a change in ambient temperature. Some vibrating gyroscopes have positive temperature coefficients, in which a drift voltage increases as the ambient temperature rises. Conversely, some vibrating gyroscopes have negative temperature coefficients, in which a drift voltage decreases as the ambient temperature rises. The gradient of a temperature characteristic differs in each vibrating gyroscope.
It is not desirable that the gradient of a temperature characteristic is large, because the characteristic of a vibrating gyroscope greatly change as the ambient temperature varies. Therefore, the upper and lower limits for a drift voltage are usually specified, and a vibrating gyroscope is determined to be acceptable when its characteristic falls in the specified zone and is determined to be unacceptable if the characteristic is out of the zone. With the use of this method, however, yield of a vibrating gyroscope falls.